Conventional magnetic storing devices such as disk drives read information from and write information to a magnetic storage medium. The disk drive typically includes a moveable arm that is positioned relative to the magnetic storage medium by a high speed linear motor or another positioning device. The arm is usually associated with multiple read and/or write channels.
Information is written to the magnetic storage medium using a write channel and a write circuit. Each write channel and circuit is capable of inducing a magnetic field with a first or second polarity adjacent to the magnetic storage medium, which stores the magnetic field. One polarity represents one digital value (such as a “1”). The opposite polarity represents the other digital value (such as a “0”). Information is read from the magnetic storage medium using a read channel and read circuit. Each read channel and circuit is capable of sensing the magnetic field stored on the magnetic storage medium.
Referring now to FIG. 1, an single-layer flexible substrate or flex circuit 10 is mounted on or otherwise connected to an arm (not shown) of a disk drive (not shown). The flex circuit 10 can be a flexible substrate as shown. While a specific outer shape of the flex circuit 10 is shown, the shape of the flex circuit 10 will vary according to the specific application.
A connector 14 can be mounted on or otherwise connected to the flex circuit 10. The connector 14 typically provides a first mating plug for receiving a second mating plug (both not shown). The second mating plug may be connected by conductors or wires to a read channel of the disk drive. A preamplifier IC 18 is also mounted on or otherwise connected to the flex circuit 10. Inductive elements 20 such as inductive coils or other devices are generally located near one end of the flex circuit 10. Typically, one or more inductive elements 20 are associated with each read and/or write channel.
The flex circuit 10 includes traces that are generally identified at 22. The traces 22 provide connections from the connector 14 to the preamplifier IC 18. Likewise, the flex circuit 10 includes traces that are generally identified at 24 (only one shown). The traces 24 provide connections from the preamplifier chip 18 to the inductive elements 20.
Referring now to FIG. 2, the flex circuit 10 typically includes a flexible substrate 30 and a patterned conductive layer 34 formed on the substrate 30 that defines the traces 22 and 24. The traces 22 and 24 relay read and/or write inputs/outputs (I/O), power and ground to and from the connector 14, the preamplifier IC 18 and/or the inductive elements 20. An insulating layer 38 may also be formed on an outer surface of the patterned conductive layer 34 to insulate the traces 22 and 24. While a single patterned conductive layer 34 is shown, multiple patterned conductive layers 34 may be provided. If multiple patterned conductive layers 34 are provided, they can optionally be interconnected by vias. While the flex circuit 10 is shown, other circuits such as printed circuit boards (PCBs) can be used.
The preamplifier IC 18 is typically formed on a wafer using photolithography. Film deposition, masking, etching and doping steps are repeated several times until all of the active devices of the preamplifier IC have been formed. Then, the individual devices in each preamplifier IC are interconnected using one or more metal layers, which are separated by insulating layers. Vias provide interconnections between the separated metal layers. After the last metal layer has been patterned, a passivation layer is deposited to protect the IC from damage and/or contamination. Openings are etched in the passivation layer of the preamplifier chip 18 to allow electrical contact to be made with the metal layers using solder bumps and traces on the flex circuit 10.
The preamplifier circuit 18 typically includes multiple read and/or write channels and requires connections to read and/or write I/O, one or more power sources, and ground. Typically, the power supply voltages are delivered to the preamplifier IC 18 using a trace and a solder bump. After reaching the IC, power distribution is performed in the metal layers of the IC. Ground and the other power supply signals are also distributed in the metal layers of the IC in a similar manner.
As the number of read and write channels increases, the number of interconnections that must be patterned in the metal layers of the IC also increases. As the number of interconnections increases, the complexity of the metal interconnection layers that are used for power and ground also increases. The increased complexity and/or additional metal layers further increase the cost of fabricating the preamplifier IC. Since power distribution is performed in the metal layers of the IC, relatively high currents and voltages must be carried by sub-micron traces in the metal layers of the IC and by the solder bumps. I2R heating in the metal layers will also increase die temperatures during operation.